1. Field of the Invention
This invention relates generally to systems for conveying articles between a plurality of stations, and more particularly, to an arrangement for transporting trays containing integrated circuits from a tray stack to a testing station, and then to a selectable one of a tray repopulation station or an output stacking station.
2. Description of the Related Art
Integrated circuit chips are provided to certain manufacturers of electronic equipment in trays which hold a plurality of such chips. In practice, the trays typically may each hold some 50 to 100 integrated circuit chips, in respective wells therein. The trays each have a respective height, and are configured to be stackable. Preferably, all of the integrated circuit chips on a tray are disposed on the same side, i.e., all tops up, and oriented identically, for example, the number "1" lead of the chip at the upper left corner of the well in the tray.
Generally, the original equipment manufacturers (OEMs) desire to test the integrated circuit chips in a variety of modes before assembling product therewith. One such test mode is optical inspection wherein a computer-assisted camera identifies the orientation of the integrated circuit chips and identify ones of the chips which are out of conformance, such as the electrical leads of each integrated circuit chip being in conformance with a predetermined specification. After inspection, the particular ones of the integrated circuit chips which are out of conformance are identified and thus precluded from being employed in the product.
Conventional systems for transporting trays of integrated circuit chips to and beyond an inspection station will generally employ a linear, or conveyor belt, approach to the task, whereby the transportation of a tray is not interruptible in mid cycle. Thus, if a disturbance should occur during cycling of the known apparatus, it will be necessary to restart the entire cycle.
In addition to the foregoing, known transport arrangements subject the trays to various mechanical shocks during handling. Such mechanical shocks disturb the placement of the integrated circuit chips in their respective wells in the trays, resulting in higher reject rates. It is to be remembered that some integrated circuit chips contain leads which are extremely close to one another, usually on the order of a few thousandths of an inch. There is therefore the ever present possibility that a mechanical shock will bend the delicate leads of the integrated circuit chips either laterally into one another, or out of their common plane, which would create difficulty with surface mounted devices in particular.
There is additionally a need for a transport system which operates smoothly so as to minimize vibration which could have a deleterious effect on the inspection process. A stable platform must be provided in order to effect the inspection, which involves high resolution patterns.
Several known arrangements employ screw drive transport systems. These known arrangements suffer from the disadvantages of drift, whereby accurate placement of the shuttle is quite difficult, particularly over extended periods of time, and limited control over shuttle acceleration and deceleration. There is a need for a system for transporting articles between stations where high placement accuracy can consistently be achieved, and also where velocity-versus-time contours can be controlled with precision over predetermined distances of shuttle travel.
Still other known article transport arrangements employ a mechanical arm which removes the article from a stack and delivers same to a testing station. In some known arrangements, a second mechanical arm removes the article from the testing station and places it in an output stack. As is well-known, a fully programmable mechanical arm requires a very significant amount of individualized software to perform even a simple function. Such systems are very complicated and require highly trained personnel to effect even minor modifications to a preprogrammed function. In the alternative, robotic arms which eliminate the need for extensive programming are generally hardware specific and cannot readily be adapted to perform new or modified functions.
It is, therefore, an object of this invention to provide a system for transporting trays of integrated circuit chips between a plurality of stations wherein the trays are reliably unstacked and the integrated circuit chips processed or inspected without being subjected to mechanical shock which would cause the integrated circuit chips on the tray to be displaced.
It is another object of this invention to provide an unstacking arrangement wherein the stacked articles are unstacked onto a conveyor arrangement, during which unstacking the motion of the articles is always controlled.
It is also an object of this invention to provide an unstacking arrangement wherein the stacked articles are not dropped onto a conveyor arrangement.
It is a further object of this invention to provide a multi-station apparatus for inspecting integrated circuit chips arranged in trays, identifying defective ones of the integrated circuit chips, and repopulating the trays with conforming ones of the integrated circuit chips.
It is additionally an object of this invention to provide a multi-station apparatus wherein inspection of integrated circuit chips arranged in trays for identifying defective ones of the integrated circuit chips is performed substantially independently of the repopulation of previously inspected one of the trays with conforming integrated circuit chips.
It is yet a further object of this invention to provide a simple and economical system for exchanging defective or non-conforming articles in a tray with conforming articles.
It is also another object of this invention to provide a system of transporting trays of integrated circuit chips to an inspection station wherein various functions of the system are independent of one another.
It is yet an additional object of this invention to provide a system of transporting trays of integrated circuit chips to a high resolution optical inspection station, wherein the transport system operates very smoothly so as to minimize vibration at the inspection station.
It is still another object of this invention to provide an article transport arrangement which can achieve a consistently high degree of accuracy in placement of a conveyor unit at preselected stations.
It is a yet further object of this invention to provide an article transport arrangement in which the acceleration characteristics of the shuttle can advantageously be controlled simply.
It is also a further object of this invention to provide an article transport arrangement which does not suffer from the drawbacks associated with screw drive systems.